Conventionally in the production of semiconductor devices, fine processing by photolithography using a photoresist has been performed. The fine processing is a processing method for forming fine convexo-concave shapes corresponding to the following pattern on the surface of a substrate by: forming a thin film of a photoresist on a semiconductor substrate such as a silicon wafer; irradiating the resultant thin film with an active ray such as an ultraviolet ray through a mask pattern in which a pattern of a semiconductor device is depicted for development; and subjecting the substrate to etching processing using the resultant photoresist pattern as a protecting film. There is disclosed a method for forming a cured film by irradiating an underlayer film of the photoresist with light (Patent Document 1).
As a pattern forming method of the next generation, nanoimprint lithography has attracted attention as one technology. The nanoimprint lithography is a method entirely different from conventional lithography using a light source. The nanoimprint lithography is a method for producing a pattern symmetric to a pattern of a template on a substrate by preparing a mold (template) having a pattern symmetric to a pattern produced beforehand and by directly pushing the mold into a resist applied on the substrate. The nanoimprint lithography is characterized in that the resolution of the nanoimprint lithography does not depend on the light source wavelength in comparison with conventional photolithography, so that an expensive apparatus such as an excimer laser exposing apparatus and an electron beam drawing apparatus is not necessary, and consequently, the cost therefor can be reduced (see, for example, Patent Document 2 and Patent Document 3).
That is, the nanoimprint lithography is a pattern forming method by: dropping by inkjet a composition of a resist for nanoimprint onto an inorganic substrate such as silicon and gallium, an oxide film, a nitride film, a quartz, a glass, or a polymer film to apply the composition thereon in a film thickness of about some ten nanometers to some micrometers; pressing a template having a fine convexo-concave shape of about some ten nanometers to some ten micrometers pattern size against the composition to pressurize the composition; irradiating the composition with light or heat-baking the composition while the composition is in a pressurized state to cure the composition; and releasing the template from the coating film to obtain a transferred pattern. Therefore, in the case of the nanoimprint lithography, for the convenience of performing light-irradiation, it is necessary that at least any one of the substrate and the template is transparent. Ordinarily, it is general to perform light-irradiation from the template side, so that, as the material for the template, there is used an optically transparent inorganic material such as quartz and sapphire or a light transmittable resin.
In order to apply the nanoimprint lithography to the imprint of a nanometer-sized pattern in a large area, there are required not only homogeneity of a pressure for pressing the template against the composition and planarity of the template or the surface of a base, but also the control of the behavior of a resist for nanoimprint that is pressed-against and flows out. In conventional semiconductor lithography, a region that is not used as an element can optionally be set on a substrate to be processed, so that a resist flow-out part can be provided using a small template in the outside of an imprint part. In the case of a semiconductor, it is satisfactory that an imprint defective part is regarded as a defective element and not used. However, for example, in the case of applying to a hard disc, the entirety functions as a device, so that a special devisal for not causing an imprint defect is necessary.
The nanoimprint lithography is a technology for patterning by a physical contact, so that as the miniaturization is progressed, there is easily caused a problem of a patterning loss such as chipping and peeling of a pattern and foreign matters caused by reattachment of the chipped or peeled pattern (see, for example, Non-patent Document 1). Peeling properties between the template and the resist for nanoimprint and adhesion between the resist for nanoimprint and the base substrate to be processed are important, so that conventionally, there has been attempted to solve a problem of defect or foreign matters by surface modifying treatment of the template or the resist.
The resist composition for nanoimprint is classified roughly into a radical crosslinking type, a cation crosslinking type, and a mixed type thereof according to the photoreaction mechanisms (see, for example, Patent Document 4, Patent Document 5, and Patent Document 6). The radical crosslinking type contains a compound derivative having an ethylenic unsaturated bond and uses generally a composition containing a polymerizable compound having a radical polymerizable methacrylate, acrylate, or vinyl group and a photocrosslinking initiator. On the other hand, the cation crosslinking type uses generally a composition containing a polymerizable compound that is a compound derivative having an epoxy or oxetane ring and a photocrosslinking initiator. When such a composition is irradiated with light, a radical or a cation that is generated from the photocrosslinking initiator attacks the ethylenic unsaturated bond or the epoxy or oxetane ring respectively, and a chain polymerization and a crosslinking reaction are progressed to form a three-dimensional network structure. When a monomer or oligomer having a multifunctional group such as a bifunctional or more group is used as a component, a crosslinked structure can be obtained.
In addition, various resists are disclosed (see Non-patent Document 2, Non-patent Document 3, and Patent Document 7).
Although the imprint lithography has previously existed, in recent years, the imprint lithography has been studied also for the formation of a fine nanopattern such as a nanopattern having some ten nanometers. However, with respect to the nanoimprint lithography, there is feared a defect caused by a direct physical contact of a resist for nanoimprint with a template (see, for example, Patent Document 8). Further, when a superposition or a large area is transferred in a lump, there is caused a problem of peeling of a resist for nanoimprint due to an adhesion failure between a substrate to be processed and a resist for nanoimprint or a problem of a variation of the film thickness of a resist for nanoimprint due to an in-plane homogeneity.
Further, in recent years, there has been caused a problem of lack of smoothness or planarity at a nano level that has become apparent according to the miniaturization of a thin line width of a pattern (see, for example, Patent Document 9). That is, following the miniaturization, a step or a via hole is formed on a substrate to be processed and a resist for nanoimprint is formed on a substrate to be processed having a large aspect ratio. Therefore, for the resist for nanoimprint used in this process, besides a characteristic of pattern forming, a characteristic of capable of controlling coating properties of a substrate around a step or a via hole, an embedding characteristic capable of filling a via hole without void, a planarizing characteristic capable of forming a planar film on the surface of a substrate, and the like are required. However, it is difficult to apply a resist for nanoimprint to a substrate having a large aspect ratio.
With respect to an attempt to add an underlayer film between a substrate to be processed and a resist for nanoimprint for solving these problems, there is conventionally no disclosure of a resist underlayer film for nanoimprint for being suitably used or no guideline for designing a material for the underlayer film. In a process for the purpose of imparting adhesion or planarity to a resist underlayer film for imprint known as an application for conventional macroimprint lithography, although some materials therefor are common with those for a resist underlayer film for nanoimprint, the above planarity is largely different from planarity characteristic on a fine pattern shape having a nanometer width or on a step or via hole having a nanometer width. Therefore, when an underlayer film applied to nanoimprint lithography is applied to nanoimprint lithography, there are frequently caused such problems as peeling of a resist for nanoimprint due to a failure of adhesion between a substrate to be processed and a resist for nanoimprint, an etching failure due to a variation of the film thickness of a resist for nanoimprint due to in-plane homogeneity, and peeling of a resist for nanoimprint due to a failure of surface smoothness or planarity.